German Auslegeschrift No. 1,069,823, discloses an apparatus relating to at least two expandable balloons provided at a distance from one another at the end on the vessel side of a treatment catheter. Each balloon is connected with a channel or duct accessible from the outside and can be inflated individually by external pressure. After the insertion of the treatment catheter into a urethra, the latter can be expanded or stretched by the inflation of the balloon. A stone forming a constricted place respectively closing the urethra, is adapted to be enclosed between the balloons. In the expanded condition of the balloons, the treatment catheter is pulled out of the urethra and the stone is removed thereby. However, this may lead to complications if the stone gets jammed in between a balloon and the inner wall of the urethra, for example, when being pulled out. The stone then has to be seized anew correctly within the area delimited by the balloons by a change of the expansion of the balloons. When pulling out the catheter, the entire urethra is thereby subjected to a strong stretching, starting from the constricted place and in particular the inner wall is stressed by strong friction pressures. This may lead to cracks or detachments at least of the inner wall of the urethra.
Furthermore, German Offenlegungsschrift No. 3,028,089 discloses use of a treatment catheter for the enlargement of constricted places in the arterial system at the end of which is attached a balloon adapted to expand its circumference to a certain dimension. This balloon is placed in the area of the constriction and is filled with a liquid by way of a catheter so that the tissue causing the constriction is pressed into the wall of the blood vessel and remains there. Frequently during the dilatation, cracks in the intima of the innermost wall of the vessel system cannot be avoided. Furthermore, the danger exists that the inner vessel layers become detached in part and obstruct the free interior space of the blood vessel, as a result of which thrombi and ischemia of the organs could result in the vessel system which are supplied by the respective blood vessel. Thus, for example, a coronary obstruction may result at the coronary arteries as a result of inadequate blood supply.